Answer :
I am going to show you the easiest, quickest and most direct way of doing it.
Take in account:
1) the result of applying a 20% discount is the same that multiplying times a factor of 0.8, which results from (100 - 20) / 100 = 80 /100 = 0.8
2) adding a 6.5% of tax is the same that multiplyiing by a factor of 1 + 6.5/100 = 1 + 0.065 = 1.065
With that
Super Sport store:
12 * 72.50 * 0.8 * 1.065 = 741.24
Double Dribble
Use that a disscount of 9% results in a factor o 0.91.
I amended the shipping fee data to 5.99 per pair of shoes.
12*54.75*0.91 + 5.99*12 = 669.75
Difference: 741.24 - 669.75 = 71.48
Take in account:
1) the result of applying a 20% discount is the same that multiplying times a factor of 0.8, which results from (100 - 20) / 100 = 80 /100 = 0.8
2) adding a 6.5% of tax is the same that multiplyiing by a factor of 1 + 6.5/100 = 1 + 0.065 = 1.065
With that
Super Sport store:
12 * 72.50 * 0.8 * 1.065 = 741.24
Double Dribble
Use that a disscount of 9% results in a factor o 0.91.
I amended the shipping fee data to 5.99 per pair of shoes.
12*54.75*0.91 + 5.99*12 = 669.75
Difference: 741.24 - 669.75 = 71.48